This invention relates to specialized amplifier systems for musical instrumentation, particularly for guitars, although its use is not limited thereto.
In performing contemporaneous popular music such as rock music, blues and the like, wherein the ensemble includes an electric lead instrument such as a guitar which at times may be playing a "background" or chordal line and, at other times, a solo or lead line, it has become customary for such instrument to be amplified differently for these two modes. In addition, it has been customary to provide for reverberation in either of these two modes. The solo line is normally referred to as the lead mode and the chordal line is normally referred to as the rhythm mode and for consistency, these terms will be used herein.
The rhythm mode refers to amplification which produces a relatively "clean" sound for the instrument in question, i.e., one which is free or substantially free of distortion; and the lead mode refers to amplification involving distortion of the sound of the instrument.
In the prior art, as exemplified for example by FIG. 1 of this application, the amplifier system comprises a series of cascaded amplifier stages for the rhythm mode and providing a "Volume I" potentiometer control at or near the input end of the cascaded stages and a "Master I" potentiometer control at the output of the final stage of the rhythm mode cascade. The amplifier system is switchable to the lead mode by switching in a further, distortion amplifier stage to the rhythm mode cascaded stages (while switching out the "Master I" control), such further stage having a "lead drive" potentiometer control at the input to the distortion stage and a "lead master" potentiometer control as the output of the distortion stage. As is conventional, the distortion stage comprises one or more high gain amplifiers operated non-linearly to provide generation of a composite signal in which half or more of the signal content may be distortion products (mostly even harmonics together with a substantial amount of odd harmonics).
Amplifier systems of this type have been very successful, but are sometimes difficult to use because the two modes are not independent. That is, the "Volume I" control sets the initial gain for both modes (or for further modes such as added reverberation or a preset attenuation of the lead mode) and this dependency makes it impossible always to obtain the desired output volumes for both a rhythm mode sound and for a lead mode sound. That is, for a very clean rhythm mode sound, the "Volume I" control must be set sufficiently low as to assure that the cascaded stages of the rhythm mode do not distort the audio signal input. This limits the maximum or full tilt distortion which may be produced in the lead mode. In consequence, some degree of compromise must be effected when setting the various interrelated volume controls. For example, assuming a very clean rhythm mode sound is to be achieved, this means that the "Volume I" control must be set to a relatively low value. If, now, a high degree of distortion is desired in the lead mode, it is limited by the setting of the "Volume I" control and the output volume of this limited distortion is likewise limited by the "Volume I" setting.
Consequently, this invention is directed to improvements in such amplifier systems.